Hello all,
I am trying to capture my graphics card at initrd, using vfio, to later pass it
through to a virtual machine. Judging by dmesg, the VFIO module does load
early, however, the card is not captured at that point and the amdgpu driver is
later loaded instead.
This is what I have in my `operating-system` config:
> (kernel-arguments '("iommu=pt" "vfio-pci.ids=1002:73bf"))
> (initrd-modules (cons* "vfio_pci" "vfio" "vfio_iommu_type1" "vfio_virqfd"
> %base-initrd-modules))
There are two video cards in the system, both AMD, but different models. The
video card of interest is in a separate IOMMU group and the <vendor id>:<device
id> combination is correct for my machine.
Best I can tell, vfio-pci.ids argument is not propagated to the module by
initramfs. See the following:
Searching online I came up against a GitHub issue for a different initramfs
generator that exhibited the same symptoms: VFIO module was loaded, kernel
arguments were correct, yet the card was not captured by the vfio driver. The
maintainer there did a great job tracking down and fixing the issue and came up
with this insight
https://github.com/anatol/booster/issues/20#issuecomment-808956316
> After reading kmod code I found that kernel does not use cmdline params for
> loadable modules. It was surprising for me. Instead it is expected that
> userspace handles cmdline parsing and provides required module params
> explicitly.
Another way to attach the correct driver to the gpu is to run a script at
initrd, which I don't know how to accomplish with Guix. This approach has the
advantage of working with two identical video cards (or disks, etc) See
https://wiki.archlinux.org/title/PCI_passthrough_via_OVMF#Using_identical_guest_and_host_GPUs
I tried following the kernel docs to rebind a different driver after boot, but
I believe this doesn't work for video cards, and hasn't worked for me.
Any help is greatly appreciated!
Links:
Kernel docs for vfio
https://www.kernel.org/doc/html/latest/driver-api/vfio.html
Arch guide for GPU passthrough
https://wiki.archlinux.org/title/PCI_passthrough_via_OVMF
Thank you!
-Nick
